1. Field of the Invention
The present invention relates to a fuel cell formed by stacking a plurality of unit cells.
2. Description of the Related Art
Fuel cells are known as devices for converting energy of a fuel into electric energy. A typical fuel cell has a stack structure formed by stacking a plurality of unit cells. Normally, each cell has a pair of electrodes that are disposed so as to sandwich an electrolyte member. An electrochemical reaction occurs when a hydrogen-containing reaction gas (fuel gas) contacts a surface of one of the pair of electrodes in each cell and an oxygen-containing gas (air) contacts a surface of the other electrode. By utilizing this electrochemical reaction, each fuel cell generates electric energy.
Japanese Patent Application Laid-open No. HEI 2-226669 discloses a fuel cell system having a plurality of fuel cell stacks divided into a plurality of blocks, with the flow rates of the gasses supplied to the fuel cells in each block being controlled.
This fuel cell system uses flow rate regulating valves to control the gas flow rates to the individual blocks. Therefore, a great number of flow rate regulating valves are required, so that the cost of the fuel cell system increases.
Furthermore, the aforementioned fuel cell system has stacks that are formed by stacking a plurality of cells, and generates electric energy by utilizing the chemical reaction occurring in each cell. Therefore, in order to optimize the power generating efficiency of the fuel cell system, it is preferable to optimize the power generating efficiency (reaction efficiency) in each fuel cell stack. However, the aforementioned system does not allow control to be performed in accordance with a parameter other than the gas flow rates to the individual fuel cell stacks, so that it is difficult to optimize the power generating efficiency in the fuel cell system.